1. Technical Field
The present disclosure relates generally to the field of pump bearings, and more particularly to bearing assemblies in down hole mud motors.
2. Background Art
Down hole mud motors are used within the oil and natural gas industry for earth boring operations. In some prior arrangements, such as the arrangement generally designated 1 as illustrated in FIG. 1, a mandrel 4 connects a drill bit through an output or drive shaft 6 and bit box 24 to a flow diverter 2 (also sometimes called a flow restrictor), the flow diverter 2 in turn connected to the rotor of the mud motor through a transmission via an upper box 5, (the transmission, drill bit and mud motor are not illustrated). In the arrangement illustrated in FIG. 1, a straight, non-tapered threaded pin 12 of mandrel 4 connects mandrel 4 to a lower flow diverter box end 14 through a straight stub acme pin. The mandrel stub acme pin, despite its rugged construction, often experiences cracks and other damage, which is undesirable. Also illustrated are an upper bearing housing 8 threadedly connected to a lower bearing housing 26 at threaded connection 28; a mud motor housing 10 threadedly connected at 11 to upper bearing housing 8; upper and lower radial bearings 16 and 18 (typically roller, ball bearing, or marine type); a thrust bearing stack 20; and a mandrel catch 22. Also illustrated are central bores 7 and 9 of the mandrel 4 and flow diverter 2, respectively, generally centered along a longitudinal axis L.
The bearings of mud motors (thrust and radial) are subjected to extreme conditions. In certain arrangements, as detailed in FIG. 1, mud motor bearing assemblies may be lubricated by drilling mud or other drilling fluid, or by dedicated oil lubricant sealed off from the drilling fluid. It would be advantageous to improve the wear resistance of bearings in mud or drilling fluid-lubricated arrangements.
U.S. Pat. No. 5,037,212 discloses thrust bearings employing a rotatable support ring fixedly attached to the drive shaft of a downhole motor. The support ring includes a plurality of diamond inserts closely spaced around the ring. The assembly further includes a stationary support ring fixedly attached to the housing of the motor. The stationary ring includes a plurality of diamond inserts spaced relatively further apart on the ring to allow cooling fluid to pass therethrough. The stationary ring is made of tungsten carbide. The '212 patent illustrates a tapered threaded connection between the mandrel and flow diverter, and a marine radial bearing integral with the flow diverter.
U.S. Pat. No. 6,416,225 discloses a mud motor bearing including at least three radial bearings to protect the flow restrictor of the bearing assembly against harmful sideways and lateral loading. U.S. Pat. No. 7,500,787, discussing the '225 patent, states that the flow restrictor is usually quite brittle, and a radial bearing is typically provided above and below the flow restrictor to protect against bending forces, necessitating two lubricated bearing chambers, where the upper bearing chamber must accommodate passages to allow drilling fluid flow between the mandrel and the housing in order to equalize pressure on either side of the upper bearing chamber. U.S. Pat. No. 6,416,225 discloses a bearing assembly having a radial bearing assembly above the flow restrictor, with a separate sealed bearing chamber from the main sealed bearing chamber. The '787 patent notes that the mandrel is also susceptible to damage by drilling loads, as well as by the severe shock and vibration incurred during drilling applications. U.S. Pat. No. 8,025,110 discloses a down hole drilling motor shaft security apparatus.
Replacement of mud motor bearings, mandrels, or components thereof are all costly operations and thus to be avoided if at all possible. The present disclosure addresses one or more of these problems.